The present invention relates to semiconductor devices employing a quantum dot structure and methods of manufacturing the same.
As dimensions of semiconductor devices scale down to nanometer scale, quantum effects are manifested in semiconductor devices. One type of quantum effect is quantization of electrical charges in the volume of the semiconductor device. For example, a semiconductor cube having a dimension of about 21.5 nm on each side has a total volume of about 104 nm3, which is 10−17 cm3. If the semiconductor cube has a dopant concentration of 1017 atoms/cm3, a single dopant atom is present in the volume of the semiconductor cube. Dopant concentration levels from about 1015 atoms/cm3 to about 1021 atoms/cm3, which are typically employed in semiconductor devices, correspond to numbers of dopant atoms from about 10−2 to about 104 in such a semiconductor cube.
By forming an isolated semiconductor island having dimensions on the order of tens of nanometers and providing a suitable doping level in the semiconductor material, the number of electrical charges in the isolated semiconductor island may be a single digit number or double digit numbers. In such a structure, quantization of electrical charge is reflected in electrical characteristics of the isolated semiconductor island. Such structures are referred to as “quantum dot” structures in which states of excitons are spatially bound in nanoscale dimensions and display quantum effects.
Scaling of conventional field effect transistors having source and drain regions that abut a body region having an opposite type of doping than the source and drain regions suffer from leakage current in an off state. As the dimensions of the field effect transistor scale down, the off-state leakage current increases. The problem becomes even more complicated when the operational voltage of the field effect transistor is also reduced. Since the voltage swing on the gate of the field effect transistor has a small magnitude, e.g., less than 1.2 V, the ratio between the on-current and the off-current of the transistor decreases with the scaling of physical dimensions and reduction of the operational voltage. A semiconductor chip containing such field effect transistors consumes a large amount of power even in an off-state. Thus, scaling of conventional field effect transistors for low power applications face a tremendous challenge.
In view of the above, there exists a need for a semiconductor device that offers an equivalent functionality of a metal-oxide-semiconductor field effect transistor (MOSFET) having dimensions on a nanometer scale and providing a low leakage current, and methods of manufacturing the same.